JP2010107796A - Charging roller, process cartridge, and electrophotographic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging member appropriate for extension in service life, increase in speed, and improvement in image quality. <P>SOLUTION: This charging roller abuts on an image carrier and charges the surface of the image carrier. The charging roller includes a core metal, an elastic layer disposed on the core metal, and a surface layer disposed on the elastic layer. The surface layer contains a binder and resin particles and graphite particles dispersed in the binder, and has projections originating in the resin particles and projections originating in the graphite particles. The projections originating in the graphite particles where the distance between the tops of the projections originating in the graphite particles and the plane including three tops of the projections originating in the resin particles adjacent to the tops of the projection originating in the graphite particles is positive occupy 80% of the total of the projections originating in the graphite particles. The average irregularity of the graphite particles forming the projections originating in the graphite particles where the distance is positive is 1.03 to 1.08. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a charging roller, a process cartridge using the same, and an electrophotographic apparatus. More specifically, the present invention relates to a charging roller for applying a voltage to charge the surface of an electrophotographic photosensitive member as an image carrier to a predetermined potential, a process cartridge and an electrophotographic apparatus using the same.

  A contact charging method has been put to practical use as a primary charging method for an electrophotographic apparatus. This is intended for low ozone and low power, and in particular, a roller charging method using a conductive roller as a charging roller is preferable and widely used in terms of charging stability.

  In the roller charging method, a conductive elastic roller is brought into pressure contact with an image carrier that is an object to be charged, and a voltage is applied to the image carrier to charge the image carrier by discharge. Specifically, a DC voltage (DC voltage) obtained by adding a required photoreceptor surface potential Vd to a discharge start voltage (about 550 V when the charging roller is pressed against the OPC photoreceptor). There is a DC charging method in which charging is performed by applying (). Furthermore, there is an AC charging method for the purpose of improving potential fluctuations due to environmental and durability fluctuations. In the AC charging method, a voltage obtained by superimposing an AC component (AC component) having a peak-to-peak voltage more than twice the discharge start voltage on a DC voltage corresponding to the required photoreceptor surface potential Vd is applied to the contact charging member. To charge.

  The DC charging method has an advantage that the cost of the power supply is generally lower than that of the AC charging method. However, compared with the AC charging method, the DC charging method has a narrow discharge area and does not have the effect of leveling the AC discharge current, and therefore, streaky charging defects due to minute uneven resistance values of the charging member are likely to occur. There was a problem.

  In view of this, a charging member used for the DC charging method has been proposed in which organic fine particles are contained in the surface layer of the charging member to form irregularities so as to improve streaky charging failure (Patent Document 1).

  However, as disclosed in Patent Document 1, in the method in which organic fine particles are contained in the surface layer of the charging member and the unevenness is formed on the surface of the charging member, external additives and the like are easily deposited in the recesses, and accordingly, the charging capability of the recesses May be reduced.

  In recent years, with the demand for higher image quality in the market, the toner has become smaller in particle size and the proportion of toner fine particles has also increased. Furthermore, various external additives are also used with the high functionalization of the toner. Therefore, the degree of contamination of the charging member tends to increase. In addition, due to demands for longer life and color, the target durable life value of the unit including the charging member and the photosensitive member has been extended, and as a result, the amount of deposits has increased, which did not occur with the previous durable number. In some cases, image defects may become apparent in the latter half of the durability life. Particularly in a low-humidity environment, the charging ability was liable to be affected by the accumulation of dirt on the concave portion of the charging member. For this reason, the effect of improving the streaky charging failure due to the formation of the unevenness may be reduced, and the image quality may be deteriorated.

  In response to this problem, it has been found that there is a tendency to improve by making the particles conductive. Patent Document 2 discloses that conductive particles are added to the surface layer of the conductive roller.

  However, Patent Document 2 did not disclose any service life extension such as maintaining charging performance for a long time as a charging member.

JP 2003-316112 A JP 2007-127777 A

  An object of the present invention is to provide a charging member suitable for extending the life, increasing the speed, and improving the image quality. Another object of the present invention is to provide an electrophotographic apparatus, a charging apparatus and a process cartridge using the charging member.

The charging roller according to the present invention is a charging roller that contacts the image carrier and charges the surface of the image carrier,
A metal core, an elastic layer provided on the metal core, and a surface layer provided on the elastic layer;
The surface layer contains a binder, resin particles and graphite particles dispersed in the binder, and has a convex portion derived from the resin particle and a convex portion derived from the graphite particle on the surface. And
The graphite particle-derived convex part having a positive distance between the vertex of the convex part derived from the graphite particle and a plane including three vertexes of the convex part derived from the resin particle adjacent to the convex part derived from the graphite particle Is 80% or more of the total number of convex portions derived from the graphite particles,
The average irregularity degree of the graphite particles forming the convex portions derived from the graphite particles having the positive distance is 1.03 or more and 1.08 or less.

The process cartridge according to the present invention is characterized in that the charging roller and the image carrier are in contact with each other and are detachable from the main body of the electrophotographic apparatus.
Furthermore, an electrophotographic apparatus according to the present invention includes the above-described charging roller and an image carrier that is in contact with the charging roller.

  In the nip of the charging roller to the photosensitive member, the convex portion derived from the resin particles regulates the press contact of the convex portion derived from the graphite particles to the photosensitive member. In addition, by increasing the number of discharge points to the photoconductor due to the protrusions derived from the graphite particles, the number of discharge opportunities increases as a result, suppressing the generation of images due to poor discharge due to dirt and preventing the occurrence of potty images due to overcharging. In addition, stable charging uniformity is maintained over a long period of time.

  As a result of intensive studies, the present inventors have found that it is effective for the above-mentioned problems to include conductive particles in the surface layer as a roughening agent for forming convex portions on the surface of the charging roller. I understood.

  As a result of intensive studies, the present inventors have suppressed the generation of defective images due to defective discharge by using graphite particles having a specific degree of unevenness as rough particles for forming convex portions on the surface of the charging roller. In addition, it was found that good charging characteristics can be maintained over a long period of time.

  In general, the discharge phenomenon is more likely to occur when the discharge electrode has a sharp shape, and the graphite particles are not spherical, and the discharge from the graphite particles is more likely to have some irregularities on the surface. It is likely to occur. The unevenness of the surface of the graphite particles increases the discharge point, and positive discharge occurs from the projections derived from the graphite particles, increasing the chances of discharge to the photoreceptor, so that dirt adheres to the surface of the charging roller due to durability. However, the discharge does not weaken. Therefore, it is estimated that uniform charging can be obtained over a long period of time.

  Furthermore, in this invention, the resin particle is added and the convex part derived from the resin particle is formed. Furthermore, the convex part derived from the graphite particles having a positive distance between the apex of the convex part derived from the graphite particles and a plane including three apexes of the convex part derived from the resin particles adjacent to the convex part is formed by the graphite particles. It is 80% or more of the total number of the convex parts derived from. As a result, direct contact of the convex portions derived from the graphite particles to the photosensitive member is restricted, deformation of the convex portions derived from the graphite particles and adhesion of dirt are reduced, and generation of a spot image due to overcharging is prevented.

(Graphite particles)
In the present invention, the graphite particles, "a substance containing carbon atoms constituting the layer structure by SP ² covalent bonds, and the half width at the peak of 1580 cm ^-1 in the Raman spectrum (from graphite) (= _delta [nu _1580. ) is 80 cm ⁻¹ or less.Δν ₁₅₈₀
Indicates the degree of graphitization and the spread of the graphite surface of the SP ² orbit, which is also an indicator of the conductivity of the graphite particles. The smaller Δν ₁₅₈₀ is, the higher the degree of graphitization, the wider the graphite surface, and the higher the conductivity. A more preferable range of Δν ₁₅₈₀ is 60 cm ⁻¹ or less. If it is this range, the effect of this invention can fully be expressed.

  Examples of such graphite particles include particles obtained by subjecting bulk mesophase pitch to graphite treatment, particles obtained by subjecting mesocarbon microbeads to graphite treatment, and the like.

  Below, the outline of the manufacturing method of the graphite particle in this invention is described.

<Particles obtained by graphite treatment of bulk mesophase pitch>
The bulk mesophase pitch can be obtained, for example, by extracting β-resin from a coal tar pitch or the like by solvent fractionation, and performing hydrogenation and heavy treatment. It can also be obtained by pulverizing after the heavy treatment and then removing the solvent-soluble component with benzene or toluene. This bulk mesophase pitch preferably has a quinoline soluble content of 95 wt% or more. When the amount less than 95 wt% is used, the inside of the particles is hardly liquid phase carbonized, and solid phase carbonization may cause the particles to remain crushed. By appropriately controlling this quinoline soluble component, the degree of unevenness of the resulting graphite particles can be controlled.

  As a method for obtaining graphite particles using mesophase pitch, first, the bulk mesophase pitch is finely pulverized and heat-treated at 200 ° C. or higher and 350 ° C. or lower in air to be lightly oxidized. By this oxidation treatment, the bulk mesophase pitch particles are infusibilized only on the surface, and melting and fusion during the graphite treatment in the next step are prevented. Moreover, the unevenness degree of the graphite particle obtained can be controlled by controlling the conditions when pulverizing. Next, the desired graphite particles are obtained by heat-treating the oxidized bulk mesophase pitch particles at 1000 ° C. or higher and 3500 ° C. or lower in an inert atmosphere such as nitrogen or argon.

<Particles obtained by graphite treatment of mesocarbon microbeads>
As a method for obtaining mesocarbon microbeads, coal-based heavy oil or petroleum-based heavy oil is heat-treated at a temperature of 300 ° C. or higher and 500 ° C. or lower and polycondensed to produce crude mesocarbon microbeads. Thereafter, the reaction product is subjected to treatments such as filtration, stationary sedimentation, and centrifugal separation to separate mesocarbon microbeads, followed by washing with a solvent such as benzene, toluene, xylene, and the like, followed by drying.

  As a method of obtaining graphite particles using these mesocarbon microbeads, first, the mesocarbon microbeads after drying are mechanically dispersed primarily with a force that does not cause destruction. This is preferable in order to obtain a uniform particle size. The mesocarbon microbeads after the primary dispersion are subjected to primary heat treatment at a temperature of 200 ° C. or higher and 1500 ° C. or lower in an inert atmosphere and carbonized. It is preferable for the carbide after the primary heat treatment to mechanically disperse the carbide with a force that does not destroy the carbide in order to prevent coalescence of the particles after the graphite treatment and to obtain a uniform particle size. The carbide that has undergone the secondary dispersion treatment is subjected to a secondary heat treatment at 1000 ° C. or more and 3500 ° C. or less in an inert atmosphere to obtain desired graphite particles.

  Further, the above-described bulk mesophase pitch and mesocarbon microbeads are used as core particles, and the surface of the core particles is coated with another bulk mesophase pitch and mesocarbon microbeads by mechanochemical treatment or the like. By firing the coated particles in an inert atmosphere, graphite particles having a desired degree of unevenness can be obtained.

<Measurement of Raman spectrum>
As for the graphite particles contained in the surface layer, the graphite particles collected from the surface layer are used as measurement samples. Moreover, about graphite particle powder, it is set as a measurement sample as it is.

The measurement method of Δν ₁₅₈₀ is performed under the following conditions.

〔conditions〕
Measuring instrument Raman spectrometer (trade name "LabRAM HR", manufactured by HORIBA JOBIN YVON)
Laser He-Ne laser (peak wavelength: 632 nm)
Filter D0.3
Hall 1000μm
Slit 100μm
Center spectrum 1500cm ^-1
Measurement time 1 second x 16 times grating 1800
Objective lens × 50

  <About the distance between the apex of the convex part derived from graphite particles and a plane including three apexes of the convex part derived from resin particles adjacent to this>

  The surface of the charging roller is observed at a visual field of 0.5 mm × 0.5 mm using a laser microscope (trade name: LSM5 PASCAL; manufactured by Carl Zeiss). By changing the wavelength of the laser to be excited and examining the spectrum of the excitation light, it is identified whether the convex portion in the field of view is derived from resin particles or graphite particles. Two-dimensional image data is obtained by scanning the laser in the XY plane within the field of view. Further, the focal point is moved in the Z direction, and the above scanning is repeated to obtain three-dimensional image data.

  Next, paying attention to the convex portions derived from any graphite particles in the field of view, three convex portions derived from the resin particles adjacent to the convex portions derived from the graphite particles are determined. Here, “adjacent” refers to a state where the sum of the distances between the vertexes of the convex portions derived from the graphite particles and the vertexes of the convex portions derived from the respective resin particles is minimized. The distance between the flat surface including the three apexes of the convex portions derived from the resin particles thus determined and the convex portions derived from the focused graphite particles is calculated from the above-described three-dimensional image data. Such an operation is performed on ten graphite particles in the field of view. Then, the same measurement is performed for 10 points in the longitudinal direction of the charging roller, and a total of 100 obtained distances between the vertexes of the convex portions derived from graphite particles and the plane including three vertexes of the convex portions derived from resin particles are measured. Examine the distribution.

  And when the apex of the convex part derived from the graphite particles is below the plane including the three apexes of the convex part derived from the resin particle, the "distance" is "positive", Define "distance" to be "negative".

  Here, if the distance between the apex of the convex part derived from graphite particles and the plane including three apexes of the convex part derived from the resin particles adjacent to the convex part derived from the graphite particle is positive, the distance of the present invention The effect can be fully demonstrated. The positive distance is preferably +3 μm or more and +20 μm or less, more preferably +10 μm or more and +20 μm or less. Within this range, while causing sufficient discharge from the projections derived from the graphite particles, the projections derived from the resin particles can sufficiently suppress the contact of the projections derived from the resin particles to the photoreceptor, and overdischarge It is possible to prevent the occurrence of a potty image due to.

  In the present invention, the convex portion derived from the graphite particles having a positive distance formed by the vertex of the convex portion derived from the graphite particles and the plane including three vertexes of the convex portions derived from the resin particles adjacent to the convex portion, The ratio (hereinafter also referred to as “frequency”) of the total number of convex portions derived from graphite particles is 80% or more. Setting the “frequency” to 80% or more has a technical significance that the charging uniformity can be maintained in almost all practical areas of the charging roller.

<Average roughness of graphite particles>
According to the above method, with respect to a convex portion derived from graphite particles having a “distance” of “positive”, a sharp blade (razor blade, cutter knife) from the apex of the convex portion in a direction parallel to the Z direction and parallel to the roller longitudinal direction. Etc.) or a microtome. The cross section of the cut surface layer is observed with an optical microscope or an electron microscope to obtain cross-sectional image data of the graphite particles. Using the image analysis software (trade name: Image-Pro PLUS, manufactured by Planetron Co., Ltd.), the ratio of the actual cross-sectional perimeter (A) and envelope perimeter (B) of the graphite particles {(A ) / (B)}, and this is defined as the degree of unevenness (see FIG. 1). Here, the envelope circumference length refers to the circumferential length when the convex portions of the graphite particle cross section are tied. Such an operation is performed for a convex portion derived from another graphite particle having a “distance” of “positive”, and an arithmetic average of a plurality of obtained unevenness degree data is defined as an average unevenness degree.

  The range of this average unevenness is 1.03 or more and 1.08 or less. If it is less than 1.03, there are too few unevenness | corrugations on the surface, and it becomes difficult to generate discharge. In particular, the discharge becomes weak in the second half of the endurance in a low-temperature and low-humidity environment, and a defective image due to defective discharge tends to occur. If it exceeds 1.08, although it is a preferable direction from the point of discharge, there are too many irregularities on the surface, and the surface layer and the elastic layer are deformed by the contact pressure when contacting the photoreceptor, and the graphite particles are It may break due to its brittleness. If the graphite particles are broken, the shape and particle size cannot be maintained, and the original function may not be exhibited.

  Moreover, as an average particle diameter of the graphite particle of this invention, a 0.2 micrometer or more thing can be mentioned as an example. A preferred range is 0.5 to 30 μm, and a more preferred range is 1 to 20 μm from the viewpoint of forming convex portions on the surface layer of the charging roller. If it is less than 0.2 μm, it becomes difficult to form a convex portion on the surface layer, and if the particle size is too large, overdischarge may occur due to the convex portion being too large.

  The method for measuring the average particle diameter of the graphite particles already contained in the surface layer is based on the projected area of the graphite particles from the cross-sectional image data of the graphite particles obtained at the time of measuring the degree of unevenness of the graphite particles. Ask for. The diameter of a circle having an area equal to this area is defined as the particle diameter of the graphite particles. Similarly, the diameter of a circle having an area equal to this area is obtained from the cross-sectional projected area of another graphite particle, and the arithmetic average of the diameters of these circles is defined as the average particle diameter.

<Measurement of particle size of graphite particles>
The particle size of the graphite particles before being contained in the surface layer is measured using a Coulter LS-230 type particle size distribution meter (manufactured by Coulter, Inc.) of a laser diffraction type particle size distribution meter. As a measuring method, an aqueous module is used, and pure water is used as a measuring solvent. The measurement system of the particle size distribution analyzer is washed with pure water for about 5 minutes, and 10 to 25 mg of sodium sulfite is added to the measurement system as an antifoaming agent to execute the background function. Next, 3 to 4 drops of a surfactant is added to 10 ml of pure water, and 5 to 25 mg of a measurement sample is further added. A sample liquid is obtained by carrying out a dispersion treatment for about 1 to 3 minutes with an ultrasonic disperser on the aqueous solution in which the sample is suspended. The sample solution was gradually added to the measurement system of the measurement device, and the sample concentration in the measurement system was adjusted so that the PIDS on the screen of the device would be 45 to 55%, and the calculation was performed from the number distribution. The number average particle diameter is determined.

It is also preferably 10 ³ Ω · cm or less 10 ^-3 Ω · cm or more as the volume resistivity of the graphite particles, and further more it is 10 ² Ω · cm or less 10 ^-1 Ω · cm or more preferable.

(Resin particles)
A known method can be used as a method for producing the resin particles, and is not particularly limited. The following method is mentioned as an example of the production method of the resin particles. First, a composition comprising a thermoplastic resin or rubber is kneaded while being heated together with a dispersion medium in a pressure kneader, and the composition is dispersed in a fine particle size in the dispersion medium. Next, the obtained kneaded product is cooled and pulverized, and then the developing solvent, which is a poor solvent for the composition and a good solvent for the dispersion medium, is mixed with the kneaded product to obtain a suspension. The target resin particles are separated from the suspension by centrifugation, filtration, or a combination of these methods. Another method for producing the resin particles may be a method of producing the resin composition by mechanical pulverization or freeze pulverization. Resin particles produced by suspension polymerization, dispersion polymerization, or the like are preferable because they have a uniform particle size and shape.

  The resin particles are made of polyamide resin, silicone resin, fluororesin, (meth) acrylic resin, styrene resin, phenol resin, polyester resin, melamine resin, urethane resin, olefin resin, epoxy resin, naphthalene resin, furan resin, xylene. Resin, divinylbenzene polymer, styrene-divinylbenzene copolymer, polyacrylonitrile resin, resins such as these copolymers, modified products, derivatives, ethylene-propylene-diene copolymer (EPDM), styrene-butadiene copolymer Rubber (SBR), silicone rubber, urethane rubber, isoprene rubber (IR), butyl rubber, acrylonitrile-butadiene copolymer rubber (NBR), chloroprene rubber (CR), epichlorohydrin rubber, polyolefin thermoplastic elastomer , Urethane thermoplastic elastomer, polystyrene thermoplastic elastomer, fluoro rubber thermoplastic elastomer, polyester thermoplastic elastomer, polyamide thermoplastic elastomer, polybutadiene thermoplastic elastomer, ethylene vinyl acetate thermoplastic elastomer, polyvinyl chloride Examples thereof include thermoplastic elastomers and thermoplastic elastomers such as chlorinated polyethylene-based thermoplastic elastomers.

  The particle size of the resin particles is preferably in the range of 1 to 30 μm. If the thickness is less than 1 μm, it becomes difficult to form a convex portion. If the thickness exceeds 30 μm, the surface of the charging roller becomes too rough and the charge becomes uneven, or the amount of toner and external additives deposited on the concave and convex portions on the surface of the charging roller It may increase. Further, if the average particle diameter of the resin particles is less than 1 μm, the contact of the convex portions derived from the graphite particles to the photoreceptor may not be sufficiently suppressed.

  In the present invention, the average particle size of the resin particles is measured using a Coulter Counter Multisizer II type (manufactured by Coulter).

  First, a 1% NaCl aqueous solution was prepared as an electrolytic solution. 0.1 to 5 ml of alkylbenzene sulfonate and 2 to 20 mg of resin particles were added to 100 to 150 ml of this electrolytic aqueous solution, and dispersion treatment was performed for about 1 to 3 minutes with an ultrasonic disperser. Then, it measured using the 100 micrometer aperture as an aperture with the multisizer type II of the Coulter counter. The volume and number distribution of resin particles were measured to calculate volume distribution and number distribution. And the particle diameter of 50% of the particle distribution on the volume basis was defined as D50, and this value was defined as the average particle diameter of the resin particles.

  In the present invention, the distance between the apex of the convex part derived from the graphite particle and the plane including three apexes of the convex part derived from the resin particle adjacent to the convex part derived from the graphite particle is derived from the graphite particle. The protrusions are 80% or more of the total number of protrusions derived from graphite particles. For that purpose, it is preferable that the particle diameter of the resin particle is larger than the particle diameter of the graphite particle.

(Configuration of the charging roller of the present invention)
The charging roller of the present invention comprises at least a cored bar, an elastic layer provided on the cored bar, and a surface layer provided on the elastic layer.

  2 to 4 are schematic sectional views showing examples of the charging roller of the present invention. FIG. 2 shows a charging roller in which an elastic layer 2 is provided on a core metal 1 and a surface layer 3 is further provided thereon. FIG. 3 shows a charging roller having an intermediate layer 21 between the elastic layer 2 and the surface layer 1. FIG. 4 shows a charging roller having intermediate layers 21 and 22 between the elastic layer 2 and the surface layer 1.

<Core>
The cored bar used in the charging roller of the present invention has conductivity, and has a function of closely supporting an elastic layer laminated thereon so that the surface of the photoreceptor can be charged to a predetermined electrostatic amount. Any one is acceptable. Examples of the material include metals such as iron, copper, aluminum, nickel, titanium, and alloys thereof (stainless steel, duralumin, brass, bronze, etc.). In addition, for the purpose of imparting scratch resistance to these surfaces, plating treatment or the like may be performed as long as the conductivity is not impaired. Further, a composite material in which carbon black or carbon fiber is hardened with plastic may be used. It is also possible to use a known material that is rigid and exhibits conductivity. Moreover, as a shape, it can also be set as the cylindrical shape which made the center part the cavity other than column shape.

<Elastic layer>
In the present invention, an elastic layer is formed on the outer periphery of the cored bar. The elastic layer ensures a nip with the photoreceptor. The elastic layer is made of an elastic body. The elastic body is usually formed by mixing a conductive agent and a polymer elastic body.

  Examples of the polymer elastic body include the following. Epichlorohydrin rubber, NBR (nitrile rubber), chloroprene rubber, urethane rubber, silicone rubber, or thermoplastic elastomer such as SBS (styrene / butadiene / styrene / block copolymer), SEBS (styrene / ethylene butylene / styrene / block copolymer).

  As the polymer elastic body, epichlorohydrin rubber is particularly preferably used. In the epichlorohydrin rubber, the polymer itself has conductivity in the middle resistance region, and can exhibit good conductivity even if the amount of the conductive agent added is small. Moreover, since the variation in electric resistance depending on the position can be reduced, it is suitably used as a polymer elastic body. Examples of epichlorohydrin rubber include the following. Epichlorohydrin homopolymer, epichlorohydrin-ethylene oxide copolymer, epichlorohydrin-allyl glycidyl ether copolymer or epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer. Of these, epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer is particularly preferably used since it exhibits stable conductivity in a medium resistance region. The epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer can control conductivity and workability by arbitrarily adjusting the degree of polymerization and composition ratio.

  The polymer elastic body may be epichlorohydrin rubber alone, but it may contain epichlorohydrin rubber as a main component and other general rubber as necessary. Other common rubbers include the following. Examples thereof include EPM (ethylene / propylene rubber), EPDM (ethylene / propylene rubber), NBR (nitrile rubber), chloroprene rubber, natural rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, urethane rubber, and silicone rubber. Further, a thermoplastic elastomer such as SBS (styrene / butadiene / styrene block copolymer) or SEBS (styrene / ethylene butylene / styrene block copolymer) may be contained. When it contains said general rubber, it is preferable that the content is 1-50 mass% with respect to the polymer elastic body whole quantity.

  As the conductive agent, an ionic conductive agent or an electronic conductive agent can be used. For the purpose of reducing unevenness of the electrical resistivity of the elastic layer, it is preferable to contain an ionic conductive agent. By uniformly dispersing the ionic conductive agent in the polymer elastic body and making the electric resistance of the elastic body uniform, uniform charging can be obtained even when the charging roller is used with only DC voltage applied. .

  The ionic conductive agent is not particularly limited as long as it is an ionic conductive agent exhibiting ionic conductivity. Examples of the ionic conductive agent include the following. Inorganic ionic substances such as lithium perchlorate, sodium perchlorate, calcium perchlorate; lauryltrimethylammonium chloride, stearyltrimethylammonium chloride, octadecyltrimethylammonium chloride, dodecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, trioctylpropylammonium Cationic surfactants such as bromide, modified aliphatic dimethylethylammonium ethosulphate; amphoteric surfactants such as lauryl betaine, stearyl betaine, dimethylalkyl lauryl betaine; tetraethylammonium perchlorate, tetrabutylammonium perchlorate, Quaternary ammonium salts such as trimethyloctadecyl ammonium perchlorate; trifluoro Organic acid lithium salts of lithium methanesulfonate or the like. These can be used alone or in combination of two or more. Among ionic conductive agents, quaternary ammonium perchlorate is particularly preferably used because of its resistance to environmental changes.

  The electronic conductive agent is not particularly limited as long as it is an electronic conductive agent exhibiting electronic conductivity. Examples of the electronic conductive agent include the following. Metal powders and fibers such as aluminum, palladium, iron, copper, silver; metal oxides such as tin oxide and zinc oxide doped with different metals; furnace black, thermal black, acetylene black, ketjen black, PAN ( Carbon black such as (polyacrylonitrile) -based carbon black.

  Examples of furnace black include the following. SAF-HS, SAF, ISAF-HS, ISAF, ISAF-LS, I-ISAF-HS, HAF-HS, HAF, HAF-LS, T-HS, T-NS, MAF, FEF, GPF, SRF-HS- HM, SRF-LM, ECF, FEF-HS. Thermal black includes FT and MT.

  Moreover, these electrically conductive agents can be used individually or in combination of 2 or more types.

  In addition, a plasticizer, a filler, a vulcanizing agent, a vulcanization accelerator, an anti-aging agent, a scorch preventing agent, a dispersing agent or a release agent can be added to the elastic body as necessary. .

  As a method for molding the elastic body, it is preferable to mix the raw materials of the above-mentioned elastic body with a hermetic mixer and mold it by a known method such as extrusion molding, injection molding, or compression molding. The elastic layer may be produced by directly molding an elastic body on the core metal, or an elastic body previously formed into a tube shape may be formed on the core metal. Note that the surface may be polished and the shape may be adjusted after the elastic layer is formed.

  An adhesive layer may be provided between the cored bar and the elastic layer. In this case, the adhesive is preferably conductive. In order to make it conductive, the adhesive may be appropriately selected from known conductive agents (for example, the above-described ionic conductive agent and electronic conductive agent), and may be used alone or in combination of two or more.

  Examples of the binder of the adhesive include thermosetting resins and thermoplastic resins, and known ones such as urethane, acrylic, polyester, polyether, and epoxy can be used.

<Crown shape>
The charging roller in the present invention preferably has a crown shape. Since the charging roller has a crown shape, the nip with respect to the photosensitive member, which is a member to be charged, can be made more uniform over the entire longitudinal direction of the charging roller.

  As a preferable shape of the charging roller in the present invention, there is a so-called crown shape in which the central portion in the longitudinal direction is the thickest and becomes narrower toward both ends in the longitudinal direction. When the charging roller is brought into contact with the photoconductor while being pressed at both ends of the cored bar, the pressure is small at the central portion in the longitudinal direction and becomes larger toward both ends in the longitudinal direction. For this reason, in a straight-shaped charging roller, density unevenness may occur between the image corresponding to the center portion and the images corresponding to both end portions. The crown shape can effectively suppress such density unevenness. The crown amount is preferably such that the difference between the outer diameter at the center and the outer diameter at a position 90 mm away from the center is not less than 30 μm and not more than 200 μm. By setting it as this range, an edge part and a center part can be made to contact | abut favorably. More specifically, if it is 30 μm or more, it is easy to avoid the state where the end portion contacts and the center portion does not contact, and if it is 200 μm or less, the center portion contacts but the end portion contacts. It is easy to escape the state of not doing.

  As a method for forming the crown shape, the elastic layer may be formed in a crown-shaped mold, or may be crowned when the elastic layer is polished.

<Surface layer>
The surface layer of the present invention includes at least a binder, resin particles dispersed in the binder, and graphite particles, and has convex portions derived from the resin particles and convex portions derived from the graphite particles on the surface. It is characterized by being.

  The content of the graphite particles in the surface layer is preferably 1 part by mass or more and 120 parts by mass or less with respect to 100 parts by mass of the binder in order to keep the charging member of the present invention having good charging ability.

  Further, the content of the resin particles in the surface layer is preferably 1 part by mass or more and 120 parts by mass or less with respect to 100 parts by mass of the binder for the same reason as described above.

  As the binder for the surface layer, a resin such as a thermosetting resin or a thermoplastic resin is used. As the binder of the surface layer of the present invention, a known binder resin can be used. Among these, fluorine resin, polyamide resin, acrylic resin, polyurethane resin, silicone resin, butyral resin, and the like are more preferable.

  Specific materials for the synthetic rubber are listed below. Ethylene-propylene-diene copolymer (EPDM), styrene-butadiene copolymer rubber (SBR), silicone rubber, urethane rubber, isoprene rubber (IR), butyl rubber, acrylonitrile-butadiene copolymer rubber (NBR), chloroprene rubber (CR ), Acrylic rubber or epichlorohydrin rubber.

  These may be used alone or in combination of two or more, or may be a copolymer.

<Other ingredients>
The surface layer can contain other materials as long as the effects of the present invention are not impaired. Examples of other materials include a conductive agent, a filler, and a release agent.

  Examples of the conductive agent include ionic conductive agents and electronic conductive agents exemplified as the conductive agent for the elastic layer.

  The surface of the conductive agent may be treated. As the surface treatment agent, for example, organosilicon compounds such as alkoxysilanes, fluoroalkylsilanes, and polysiloxanes, various titanate-based, aluminate-based, or zirconate-based coupling agents, oligomers, or polymer compounds can be used. These may be used alone or in combination of two or more. Preferred are organosilicon compounds such as alkoxysilane and polysiloxane, and various coupling agents of titanate, aluminate or zirconate.

  When carbon black is used as a conductive agent, it is preferably used as composite conductive fine particles in which metal oxide fine particles are coated with carbon black. Since carbon black forms a structure, it tends to be difficult for the carbon black to exist uniformly with respect to the binder. When carbon black is used as composite conductive fine particles coated with a metal oxide, the conductive agent can be uniformly present in the binder, and the volume resistivity can be controlled more easily.

  Specifically, the metal oxide fine particles used for this purpose include zinc oxide, tin oxide, indium oxide, titanium oxide (titanium dioxide, titanium monoxide, etc.), iron oxide, silica, alumina, magnesium oxide, zirconium oxide. Etc.

  The metal oxide fine particles are preferably surface-treated. As the surface treatment, organosilicon compounds such as alkoxysilanes, fluoroalkylsilanes, polysiloxanes, etc., various titanate, aluminate or zirconate coupling agents, oligomers or polymer compounds can be used. These may use 1 type or may use 2 or more types together.

  As the mold release agent, those having low surface energy, those having slidability, and the like can be used. By including a release agent in the surface layer, the relative movement between the charging roller and the photosensitive member becomes smooth, and the occurrence of an irregular movement state such as stick-slip is reduced. As a result, the occurrence of irregular wear on the surface of the charging roller, the generation of abnormal noise, etc. are suppressed. When the release agent is a liquid, it also acts as a leveling agent when forming the surface layer.

  Specifically, metal oxides such as molybdenum disulfide, tungsten disulfide, boron nitride, and lead monoxide. In addition, oil- or solid-state (release resin or powder thereof, a part of the polymer into which a part having release property is introduced) silicon or fluorine-containing compound, wax, higher fatty acid, salt thereof , Esters and other derivatives can also be used.

  In the present invention, the conductive agent added to the elastic layer or the surface layer is different from graphite particles and resin particles and has a particle size of less than 0.2 μm. If it is this range, it will be easy to control the volume resistivity of an elastic layer and a surface layer.

  The surface layer of the present invention preferably has a thickness of 0.1 μm or more and 100 μm or less. More preferably, they are 1 micrometer or more and 50 micrometers or less.

  The thickness of the surface layer can be measured by cutting the roller cross section with a sharp blade and observing with an optical microscope or an electron microscope.

  The surface layer may be further subjected to a surface treatment. Examples of the surface treatment include a surface processing treatment using UV or electron beam, and a surface modification treatment for adhering and / or impregnating a compound or the like on the surface.

<Method for forming surface layer>
As a method for forming the surface layer of the present invention, a method in which a coating material in which graphite particles and resin particles are dispersed in a binder is applied on the elastic layer is preferable. If it is this method, it will be easy to form the convex part derived from a graphite particle and the convex part derived from a resin particle in a surface layer. Moreover, it is easy to control the degree of unevenness of the graphite particles in the surface layer and the relationship between the height of the protrusions derived from the graphite particles and the height of the protrusions derived from the resin particles.

<Roughness of charging roller surface>
As the surface roughness of the surface layer, the ten-point average roughness Rzjis and the surface irregularity average distance Sm according to JIS B0601-2001 are preferably in the following ranges.
2 μm ≦ Rzjis ≦ 20 μm
15 μm ≦ Sm ≦ 150 μm

  In order to obtain a charging roller having a surface roughness in the above range, the surface roughness of the elastic layer, the film thickness of the surface layer, the average particle diameter of graphite particles and resin particles, and the addition amount are adjusted. By setting the surface roughness Rzjis and the average unevenness interval Sm of the charging roller within these ranges, the contact state between the charging roller and the electrophotographic photosensitive member can be made more stable. This is more preferable because it is easy to uniformly charge the photosensitive member.

<Hardness of charging roller>
The suitable hardness of the charging roller of the present invention is preferably a micro hardness of 30 ° or more and 80 ° or less, and more preferably 45 ° or more and 65 ° or less. Within this range, even when the charging roller is in contact with the photosensitive member for a long time, the contact mark does not appear in the image, which is preferable. In addition, "micro hardness" is the hardness of the rubber member measured using the micro area | region rubber hardness meter (Brand name "Asker micro rubber hardness meter MD-1 type | mold", the Kobunshi Keiki Co., Ltd. make). . In the present invention, the hardness meter is set to a value measured in a 10 N peak hold mode for a charging roller left in a 23 ° C./55% RH (NN) environment for 12 hours or more.

<Electric resistance of charging roller>
The charging roller of the present invention usually has an electric resistance of 1 × 10 ² Ω or more and 1 × 10 ¹⁰ Ω or less in an environment of 23 ° C. and 50% RH in order to ensure charging of the photoreceptor. More preferably.

  As an example, FIG. 5 shows a method for measuring the electrical resistance of the charging roller. Both ends of the cored bar 1 are brought into contact with the columnar metal 32 having the same curvature as that of the photoconductor by bearings 33a and 33b under load. In this state, the cylindrical metal 32 is rotated by a motor (not shown), and a DC voltage of −200 V is applied from the stabilized power supply 34 while the charging roller 5 that is in contact with the rotation is driven to rotate. The current flowing at this time is measured by an ammeter 35, and the resistance of the charging roller is calculated. Here, the load is 4.9 N, the metal cylinder has a diameter of 30 mm, and the rotation of the metal cylinder has a peripheral speed of 45 mm / sec.

In the present invention, the volume resistivity of the powder such as graphite particles and conductive agent is 23 ° C./50% RH environment, using a resistance measuring device “Loresta-GP” (trade name, manufactured by Mitsubishi Chemical Corporation) as a sample. The measured value when a voltage of 10 V is applied. In addition, as a sample to be measured, a sample compressed by applying a pressure of 10.1 MPa (10 ² kgf / cm ² ) was used.

(Electrophotographic equipment)
FIG. 6 shows a schematic configuration of the image forming apparatus according to the present invention.

  The image forming apparatus includes a photosensitive member, a charging device that charges the photosensitive member, a latent image forming device that performs exposure, a developing device that develops a toner image, a transfer device that transfers to a transfer material, and a cleaning that collects transfer toner on the photosensitive member. And a fixing device for fixing a toner image.

  The photoreceptor 4 is a rotary drum type having a photosensitive layer on a conductive substrate. The photoreceptor is driven to rotate in the direction of the arrow at a predetermined peripheral speed (process speed).

  The charging device includes a contact-type charging roller 5 that is placed in contact with the photosensitive member by being brought into contact with the photosensitive member with a predetermined pressing force. The charging roller 5 is driven rotation that rotates in accordance with the rotation of the photosensitive member, and charges the photosensitive member to a predetermined potential by applying a predetermined DC voltage from a charging power source. For example, an exposure apparatus such as a laser beam scanner is used as the latent image forming apparatus 11 that forms an electrostatic latent image on the photosensitive member. An electrostatic latent image is formed by performing exposure corresponding to image information on a uniformly charged photoconductor.

  The developing device has a contact-type developing roller 6 disposed close to or in contact with the photoreceptor. The toner electrostatically processed to the same polarity as the photosensitive member charge polarity is developed by reversal development to visualize and develop the electrostatic latent image into a toner image.

The transfer device has a contact-type transfer roller 8. The toner image is transferred from the photoreceptor to a transfer material such as plain paper (the transfer material is conveyed by a paper feed system having a conveying member).

  The cleaning device includes a blade-type cleaning member 10 and a collection container, and after transfer, mechanically scrapes and collects transfer residual toner remaining on the photosensitive member.

  Here, it is also possible to remove the cleaning device by adopting a development simultaneous cleaning system in which the transfer device collects the transfer residual toner.

  The fixing device is composed of a heated roll or the like, fixes the transferred toner image, and discharges the toner image outside the apparatus.

(Process cartridge)
The process cartridge of the present invention is obtained by integrating the charging roller of the present invention at least with an image carrier. Specifically, a process cartridge (FIG. 7) designed to be detachable from the electrophotographic apparatus main body by integrating a photoconductor as an image carrier, a charging device including a charging roller of the present invention, a developing device, and a cleaning device. ) Can also be used.

  Hereinafter, the present invention will be described in more detail with reference to specific examples, but the technical scope of the present invention is not limited thereto.

<Production example of graphite particles>
<Production example of graphite particles 1 to 3>
Β-Resin was extracted from coal tar pitch by solvent fractionation, and this was subjected to weighting treatment by hydrogenation. Subsequently, bulk mesophase pitch was obtained by removing solvent-soluble components with toluene. After this bulk mesophase pitch was mechanically pulverized, it was heated to 270 ° C. in air at a temperature rising rate of 300 ° C./h, and then subjected to an oxidation treatment. This was classified into fine powders having an average particle size of 20 μm, 3 μm, 1 μm and less than 1 μm. Among these, particles having an average particle diameter of 20 μm, 3 μm, and 1 μm are used as core particles.

  Fine powder having a particle size of less than 1 μm generated during classification is used as the coated particles.

  100 parts by mass of core particles having an average particle diameter of 20 μm and 25 parts by mass of bulk mesophase pitch having a particle diameter of less than 1 μm are mixed uniformly, and then dry-mixed (mechanochemical) in a raikai machine (automatic mortar, manufactured by Ishikawa Factory). Treatment). As a result, pitch-coated spherical particles were obtained in which the surface of the bulk mesophase pitch particles serving as the core was uniformly coated with a bulk mesophase pitch having a smaller particle size.

  Next, the pitch-coated spherical particles were heated to 1000 ° C. at a temperature rising rate of 200 ° C./hr in a nitrogen atmosphere, held for 1 hour, and fired to obtain graphite particles 1.

Similarly, 3 μm core particles and 1 μm core particles pitch-coated particles were fired in the same manner as above to obtain graphite particles 2 and 3. Table 1 shows the full width at half maximum of the peak intensity at 1580 cm ⁻¹ of the Raman spectrum of the obtained graphite particles.

<Production example of graphite particles 4 to 6>
Coal heavy oil was heat-treated, and the generated crude mesocarbon microbeads were centrifuged, washed with benzene, purified and dried. Subsequently, mechanical dispersion was performed with an atomizer mill to obtain mesocarbon microbeads. The mesocarbon microbeads were heated to 1200 ° C. at a temperature rising rate of 600 ° C./h in a nitrogen atmosphere, and then subjected to secondary dispersion in an atomizer mill. At this time, the average particle size was adjusted to be about 6 μm. The mesocarbon microbeads 100 parts by mass are mixed with 25 parts by mass of a bulk mesophase pitch having a particle size of less than 1 μm similar to those used in Production Examples 1 to 3, and then used with a raikai machine (automatic mortar, manufactured by Ishikawa Factory). Then, dry mixing treatment (mechanochemical treatment) was performed. As a result, pitch-coated spherical particles were obtained in which the surface of the bulk mesophase pitch particles serving as the core was uniformly coated with a bulk mesophase pitch having a smaller particle size.

The obtained pitch-coated spherical particles were heated to 2800 ° C. at a heating rate of 1400 ° C./h in a nitrogen atmosphere, and heat-treated at 2800 ° C. for 15 minutes. Further, classification treatment was performed to obtain graphite particles 4, 5, and 6 having average particle diameters of 20 μm, 6 μm, and 1 μm. Table 1 shows the full width at half maximum of the peak intensity at 1580 cm ⁻¹ of the Raman spectrum of the obtained graphite particles.

<Production example of graphite particles 7 and 8>
Β-Resin was extracted from coal tar pitch by solvent fractionation, and this was subjected to weighting treatment by hydrogenation. Subsequently, bulk mesophase pitch was obtained by removing solvent-soluble components with toluene. After this bulk mesophase pitch was mechanically pulverized, the temperature was increased to 280 ° C. in air at a temperature increase rate of 300 ° C./h, and an oxidation treatment was performed. During the pulverization, the average particle size was adjusted to about 3 μm. Then, it heated up to 2500 degreeC in nitrogen atmosphere, and heat-processed at 2500 degreeC for 15 minutes. Further, classification treatment was performed to obtain graphite particles 7 and 8 having average particle diameters of 20 μm and 1 μm, respectively. Table 1 shows the full width at half maximum of the peak intensity at 1580 cm ⁻¹ of the Raman spectrum of the obtained graphite particles.

<Production example of graphite particles 9 and 10>
The coal-based heavy oil was heat-treated at 400 ° C. and polycondensed to produce crude mesocarbon microbeads. Then, the mesocarbon microbeads were separated by centrifugation, washed with benzene, and further dried.

Thereafter, the mesocarbon microbeads were mechanically primary dispersed with an atomizer mill, subjected to primary heat treatment at 1200 ° C. in a nitrogen atmosphere, and further subjected to secondary dispersion with an atomizer mill. The obtained dispersion was heated to 2800 ° C. at a heating rate of 1000 ° C./h under a nitrogen atmosphere, and subjected to secondary heat treatment at 2800 ° C. for 15 minutes. The mesocarbon microbeads thus obtained were subjected to a spheronization treatment using a hybridizer (manufactured by Nara Machinery Co., Ltd.) to produce substantially spherical mesocarbon microbeads. Further classification treatment was performed to obtain graphite particles 9 and 10 having average particle diameters of 5 μm and 1 μm, respectively. Table 1 shows the full width at half maximum of the peak intensity at 1580 cm ⁻¹ of the Raman spectrum of the obtained graphite particles.

<Production example of graphite particles 11 and 12>
The β-resin was extracted from the coal tar pitch by solvent fractionation and subjected to weighting treatment by hydrogenation to obtain a bulk mesophase pitch. Subsequently, the bulk mesophase pitch was mechanically pulverized without removing the solvent-soluble component, and then heated to 270 ° C. at a temperature rising rate of 300 ° C./h in the air to be oxidized. During the pulverization, the average particle size was adjusted to about 3 μm. Subsequently, in a nitrogen atmosphere, the temperature was increased to 3000 ° C. at a temperature increase rate of 1500 ° C./h, and heat treatment was performed at 3000 ° C. for 15 minutes. Further, classification treatment was performed to obtain graphite particles 11 and 12 having average particle diameters of 6 μm and 1 μm, respectively. Table 1 shows the full width at half maximum of the peak intensity at 1580 cm ⁻¹ of the Raman spectrum of the obtained graphite particles.

<Resin particles used in this example>
Resin particles 1: cross-linked polymethyl methacrylate resin particles (manufactured by Sekisui Plastics Co., Ltd., Techpolymer MBX-20 (trade name), average particle size 20 μm)
Resin particles 2: Cross-linked urethane resin particles (manufactured by Negami Kogyo Co., Ltd., Art Pearl C-400 (trade name), average particle diameter: 14 μm)
Resin particles 3: Cross-linked polymethyl methacrylate resin particles (manufactured by Sekisui Plastics Co., Ltd., Techpolymer MBX-12 (trade name), average particle size: 12 μm)
Resin particle 4: Cross-linked polymethylmethacrylate resin particle (manufactured by Soken Chemical Co., Ltd., Chemisnow MX-1000 (trade name), average particle size 10 μm)
Resin particles 5: cross-linked polymethylmethacrylate resin particles, average particle diameter of 3 μm
Resin particle 6: cross-linked polymethylmethacrylate resin particle, average particle size 25 μm
Resin particles 7: Silicone resin particles (Momentive Performance Materials Japan G.K., Tospearl 120A (trade name), average particle diameter 2 μm)
Resin particle 8: Cross-linked polymethyl methacrylate resin particle (manufactured by Sekisui Plastics Co., Ltd., Techpolymer MBX-5 (trade name), average particle diameter 5 μm)

[Preparation of composite conductive fine particles]
To 7.0 kg of silica particles (average particle diameter 12.5 nm, volume resistivity 1.4 × 10 ¹² Ωcm), 140 g of methyl hydrogen polysiloxane was added while operating the edge runner, and 588 N / cm (60 kg / cm ) Was mixed and stirred for 30 minutes. The stirring speed at this time was 22 rpm.

Into this, 7.0 kg of carbon black particles (average particle diameter 28 nm, volume resistivity 1.2 × 10 ² Ωcm) was added over 10 minutes while operating the edge runner. Thereafter, the mixture was stirred for 60 minutes with a linear load of 588 N / cm (60 kg / cm). In this way, after carbon black was adhered to the surface of the silica particles coated with methylhydrogenpolysiloxane, drying was performed at 80 ° C. for 60 minutes using a dryer, to obtain composite conductive fine particles. The stirring speed at this time was 22 rpm. The obtained composite conductive fine particles had an average particle diameter of 15 nm and a volume resistivity of 2.3 × 10 ² Ωcm.

[Preparation of surface-treated titanium oxide fine particles]
1000 g of acicular rutile-type titanium oxide fine particles (average particle size 15 nm, length: width = 3: 1, volume resistivity 5.2 × 10 ¹⁰ Ωcm), 100 g of isobutyltrimethoxysilane as a surface treatment agent, and 3000 g of toluene as a solvent To prepare a slurry.

  This slurry was mixed with a stirrer for 30 minutes, and then supplied to Viscomill in which 80% of the effective internal volume was filled with glass beads having an average particle diameter of 0.8 mm, and wet crushing was performed at a temperature of 35 ± 5 ° C. .

  Toluene was removed from the slurry obtained by wet pulverization by vacuum distillation (bath temperature: 110 ° C., product temperature: 30-60 ° C., degree of vacuum: about 100 Torr) using a kneader, and the surface was kept at 120 ° C. for 2 hours. The treating agent was baked. The fine particles subjected to the baking treatment were cooled to room temperature and then pulverized using a pin mill to obtain surface-treated titanium oxide fine particles.

[Production of cored bar with elastic layer]
A thermosetting adhesive "Metaloc U-20" (trade name, manufactured by Toyo Chemical Laboratory Co., Ltd.) is applied to a stainless steel round bar with a diameter of 6mm and a length of 252.5mm. did.

The following components were added to 100 parts by mass of epichlorohydrin rubber and kneaded for 10 minutes in a closed mixer adjusted to 50 ° C. to prepare a raw material compound.
-60 parts by weight of calcium carbonate-8 parts by weight of aliphatic polyester plasticizer-1 part by weight of zinc stearate-2-mercaptobenzimidazole (MB) (anti-aging agent) 0.5 parts by weight-2 parts by weight of zinc oxide Class ammonium salt 2 parts by mass Carbon black (average particle size 100 nm, volume resistivity 0.1 Ωcm) 5 parts by mass

  To this, 0.8 parts by mass of sulfur as a vulcanizing agent, 1 part by mass of dibenzothiazyl sulfite (DM) and 0.5 parts by mass of tetramethylthiuram monosulfide (TS) as vulcanization accelerators were cooled to 20 ° C. The elastic layer compound was obtained by kneading for 15 minutes using the two-roll mill.

  Along with the metal core, the elastic layer compound was extruded by an extrusion molding machine with a crosshead and molded into a roller shape having an outer diameter of about 9 mm. Next, vulcanization and curing of the adhesive were performed in an electric oven at 160 ° C. for 1 hour. Thereafter, both ends of the rubber were cut off to make the rubber length 232 mm. Further, the surface was polished so that the outer diameter of the roller at the central part of the roller was 8.5 mm, and an elastic layer was formed on the metal core to obtain a metal core with an elastic layer.

<Preparation of charging roller 1>
Methyl isobutyl ketone was added to caprolactone-modified acrylic polyol solution “Placcel DC2016” (trade name, manufactured by Daicel Chemical Industries, Ltd.) to adjust the solid content to 16% by mass.

The following components were added to 625 parts by mass of this solution (acrylic polyol solid content: 100 parts by mass) to prepare a mixed solution.
-Composite conductive fine particles 45 parts by mass-Surface-treated titanium oxide fine particles 30 parts by mass-Modified dimethyl silicone oil 0.08 parts by mass-Block isocyanate mixture 80.14 parts by mass

  At this time, the blocked isocyanate mixture is a 7: 3 mixture of each butanone oxime block of hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI). The amount of isocyanate was “NCO / OH = 1.0”.

  The modified dimethyl silicone oil used was “SH28PA” (trade name, manufactured by Toray Dow Corning Silicone Co., Ltd.).

  210 g of the mixed solution was put in a glass bottle with an internal volume of 450 mL together with 200 g of glass beads having an average particle diameter of 0.8 mm as a medium, and dispersed for 48 hours using a paint shaker disperser (this is referred to as primary dispersion).

  Next, 16.4 g of resin particles 1 (60 parts by mass with respect to 100 parts by mass of the acrylic polyol solid content) was added and then dispersed for 1 hour (this is referred to as secondary dispersion). Finally, 2.05 g of graphite particles 2 (equivalent to 7.5 parts by mass with respect to 100 parts by mass of the acrylic polyol solid content) was added and dispersed for 5 minutes (this is referred to as tertiary dispersion). Thereafter, the glass beads were removed by filtration to obtain a surface layer coating solution having a viscosity of 10 mPa · s.

  The surface layer coating solution was dipped onto the cored bar with the elastic layer obtained as described above once. After air drying at room temperature for 30 minutes or more, it was dried with a hot air circulating dryer at 80 ° C. for 1 hour and further at 160 ° C. for 1 hour to form a surface layer having a thickness of 15 μm on the elastic layer. In this way, a charging roller 1 having an elastic layer and a surface layer on the core metal was obtained. The dipping coating immersion time was 9 seconds, and the dipping coating lifting speed was an initial speed of 20 mm / s and a final speed of 2 mm / s, and the speed was changed linearly with respect to the time.

  The crown amount of the obtained charging roller 1 (the difference in the outer diameter at a position 90 mm away from the central portion and the central portion) was 115 μm.

  The obtained charging roller 1 is derived from graphite particles having a positive distance between the apex of the convex portion derived from the graphite particles and a plane including three apexes of the convex portions derived from the resin particles adjacent to the convex portion. The ratio (frequency) of the protrusions to the total number of protrusions derived from graphite particles was 95%. The average value of the positive distance was 17 μm.

  Table 2 shows the results of measuring the average roughness, Rzjis, and Sm of the graphite particles in the surface layer of the charging roller 1 according to the measurement method described above.

<Preparation of charging roller 2>
Acetone was added to 100 parts by mass of polyvinylidene fluoride resin (PVDF, trade name: Kyner 7201, manufactured by Arkema) so that the resin concentration was 15%, and the resin was dissolved. To this resin solution, 100 parts by weight of conductive zinc oxide (manufactured by Hakusuitec Co., Ltd., passet CK (trade name)) and 100 parts by weight of glass beads having an average particle diameter of 0.8 mm as a dispersion medium are added. And dispersed for 6 hours.

  Subsequently, after adding 60 mass parts of resin particles 1, it disperse | distributed for 1 hour. Thereafter, after further adding 7.5 parts by mass of graphite particles 2, the mixture was dispersed for 5 minutes.

  After the dispersion, the glass beads were separated by filtration to obtain a coating material for forming a surface layer.

  The coating material obtained as described above was dipped in the same manner as in Example 1 to obtain a charging roller 2.

  The obtained charging roller 2 is derived from graphite particles having a positive distance between the apex of the convex portion derived from the graphite particles and a plane including three apexes of the convex portions derived from the resin particles adjacent to the convex portion. The ratio (frequency) of the protrusions to the total number of protrusions derived from the graphite particles was 92%. The average value of the positive distance was 17 μm.

  Table 2 shows the results of measuring the average roughness, Rzjis, and Sm of the graphite particles in the surface layer of the charging roller 2 according to the measurement method described above.

<Preparation of charging roller 3>
Ethanol was added to 100 parts by mass of N-methoxymethylated nylon so that the resin concentration was 15%, and the resin was dissolved. To this resin solution, 15 parts by mass of carbon black (Carbon Black for Mitsubishi Color # 52 (trade name)) is added, and 100 parts by mass of glass beads having an average particle diameter of 0.8 mm are added as dispersion media to this paint shaker. It was dispersed for 50 hours using a disperser.

  Subsequently, after adding 60 mass parts of resin particles 1, it disperse | distributed for 1 hour. Thereafter, after further adding 7.5 parts by mass of graphite particles 2, the mixture was dispersed for 5 minutes.

  After the dispersion, the glass beads were separated by filtration to obtain a coating material for forming a surface layer.

The coating material obtained as described above was dipped in the same manner as in Example 1 to obtain a charging roller 3.

  The obtained charging roller 3 is derived from graphite particles having a positive distance between the apex of the convex portion derived from the graphite particles and a plane including three apexes of the convex portions derived from the resin particles adjacent to the convex portion. The ratio (frequency) of the protrusions to the total number of protrusions derived from the graphite particles was 90%. The average value of the positive distance was 17 μm.

  Table 2 shows the results of measuring the average roughness, Rzjis, and Sm of the graphite particles in the surface layer of the charging roller 3 according to the measurement method described above.

<Preparation of charging roller 4>
An acrylic resin (glass transition temperature: 18 ° C.) containing HEMA (2-hydroxyethyl methacrylate) was dissolved in a methyl ethyl ketone (MEK) solvent. To this, 60 parts by mass of alcohol-modified silicone oil “FZ-3711” (Toray Dow Corning) prepolymerized with bifunctional isocyanate was added with respect to 100 parts by mass of acrylic resin. Furthermore, 35 parts by mass of carbon black (Denka Black powder (trade name) manufactured by Denki Kagaku Kogyo Co., Ltd.) is added as a conductive agent, and 100 parts by mass of glass beads having an average particle diameter of 0.8 mm are added thereto as a dispersion medium And dispersed for 50 hours using a paint shaker disperser.

  Subsequently, after adding 60 mass parts of resin particles 1, it disperse | distributed for 1 hour. Thereafter, after further adding 7.5 parts by mass of graphite particles 2, the mixture was dispersed for 5 minutes.

  After the dispersion, the glass beads were separated by filtration to obtain a coating material for forming a surface layer.

  The coating material obtained as described above was dipped in the same manner as in Example 1 to obtain a charging roller 4.

  The obtained charging roller 4 is derived from graphite particles having a positive distance between the apex of the convex portion derived from the graphite particles and a plane including three apexes of the convex portions derived from the resin particles adjacent to the convex portion. The ratio (frequency) of the convex portion to the total number of convex portions derived from the graphite particles was 94%. The average value of the positive distance was 17 μm.

  Table 2 shows the results of measuring the average roughness, Rzjis, and Sm of the graphite particles in the surface layer of the charging roller 4 according to the measurement method described above.

<Production of charging rollers 5 to 24>
Charging rollers 5 to 24 were produced in the same manner as the charging roller 1 except that the types and addition amounts of the graphite particles and the resin particles were changed to those shown in Table 1. For the charging roller 23, only the resin particles were added without adding the graphite particles.

  About the obtained charging rollers 5 to 22, graphite particles having a positive distance between the vertex of the convex portion derived from the graphite particles and a plane including three vertexes of the convex portions derived from the resin particles adjacent to the convex portion The ratio (frequency) of the protrusions derived from the total number of the protrusions derived from the graphite particles was 80% or more. The frequency measurements are shown in Table 2. Since the charging roller 23 did not add graphite particles, the frequency was 0%, and the frequency of the charging roller 24 was 10%.

  Further, with respect to the charging rollers 5 to 22, the average values of the distances formed by the vertexes of the convex portions derived from the graphite particles and the plane including three vertexes of the convex portions derived from the resin particles adjacent to the convex portions are shown in Table 2. Show. Since the charging roller 23 did not add graphite particles, the distance could not be measured, and the distance of the charging roller 24 was a negative value of −3 μm.

  Table 2 shows the results of measuring the average roughness, Rzjis, and Sm of the graphite particles in the surface layers of the obtained charging rollers 5 to 22 and 24 in accordance with the above-described measuring method.

Example 1
[Image Evaluation of Charging Roller 1]
<Stain adhesion promotion test>
The produced charging roller was mounted on a black cartridge of an electrophotographic apparatus (LBP5400, manufactured by Canon Inc.) and incorporated into an electrophotographic apparatus (LBP5400, manufactured by Canon Inc.) as an electrophotographic apparatus having the configuration shown in FIG. Then, under a 23 ° C./50% RH environment (NN environment), after printing 50 single-color solid images, one solid white image was printed. This was repeated 6 times, and a total of 300 single-color solid images were printed to obtain a charging roller for which the surface was forcibly adhered with toner or external additives in advance. Note that -1100 V was applied only to the DC voltage to the charging roller.

  The charging roller subjected to the dirt adhesion promotion test as described above was mounted on another black cartridge, and the durability test was performed.

<Durability Image Evaluation (Charge Uniformity (Charge Horizontal Streaks))>
By modifying the electrophotographic apparatus (LBP5400, manufactured by Canon Inc.), the process speed was set to 200 mm / s to increase the speed. Using this electrophotographic apparatus, after outputting one image and stopping the rotation of the electrophotographic apparatus, the operation of restarting the image forming operation is repeated (intermittent durability at a printing rate of 1%). An output durability test was conducted.

  The above test was performed in two environments of 23 ° C./50% RH (NN environment) and 15 ° C./10% RH (LL environment). During the endurance test, halftone images were output at the 1000th, 3000th, and 5000th time points, and the state of occurrence of charged horizontal streak images was evaluated from the images. The evaluation of the occurrence state was performed according to the following evaluation criteria.

<Evaluation criteria for charged horizontal streak images>
◎: Not generated ○: Only slight occurrence, no problem in practical use △: Occurrence is observed in a part of the image, and the image quality is deteriorated ×: The image is generated in the whole image, and the image quality is remarkably deteriorated

  The evaluation results are shown in Table 1. The charged horizontal streak image was not generated during the durability evaluation, and a good image could be maintained.

  Further, the occurrence of a spot image in a halftone image due to overcharging at the time of printing 5000 sheets was evaluated.

<Pochi images caused by overcharging>
◎: No occurrence of potty image due to overcharge ○: Half-tone image has slight spot-like image defects ×: Spot-like image defects are conspicuous

  As a result, there was no occurrence of a sticky image due to overcharging, and a good image could be maintained.

(Examples 2 to 18)
Image evaluation was performed in the same manner as in Example 1 except that the charging rollers 2 to 18 were used. The results are shown in Table 2.

(Comparative Examples 1-6)
Image evaluation was performed in the same manner as in Example 1 except that the charging rollers 19 to 24 were used. The results are shown in Table 2.

<Evaluation results>
In Examples 2 to 4, regardless of the binder of the surface layer, it was confirmed that the charged horizontal streak image was not generated during the durability evaluation and the good image was maintained by adopting the configuration of the present invention. . In addition, it was confirmed that no sticky image was generated due to overcharging after printing 5000 sheets, and a good image was maintained.

  In Example 5, although the degree of unevenness of the graphite particles is slightly smaller than in Example 1, slight horizontal streaks occurred at the time of printing 5000 sheets under the LL environment, which is a disadvantageous condition for charging uniformity. There was no problem in practical use.

  In Example 6, the degree of unevenness of the graphite particles was slightly smaller than in Example 5, and slight horizontal streaks occurred at the time of printing 3000 sheets under the LL environment, but there was no problem in actual use. Met.

  In Example 7, the charged horizontal streak image was not generated during the durability evaluation, and it was confirmed that a good image was maintained. However, because of the small difference in height between the protrusions of less than 10 μm, slight spot-like image defects were observed in the halftone image under the LL environment. However, there was no problem in actual use.

  In Example 8, although the degree of unevenness of the graphite particles is slightly smaller than in Example 7, slight horizontal streaks occurred at the time of printing 5000 sheets under the LL environment, which is a disadvantageous condition for charging uniformity. There was no problem in practical use.

  In Example 9, the degree of unevenness of the graphite particles was slightly smaller than in Example 8, and slight horizontal streaks occurred at the time of printing 3000 sheets under the LL environment, but there was no problem in actual use. Met.

  In Example 10, the charged horizontal streak image was not generated during the durability evaluation, and it was confirmed that a good image was maintained. However, the difference in the height of the convex part was less than 3 μm, or there was a slight point-like image defect in the halftone image in both NN and LL environments, but there was no problem in practical use. there were.

  In Example 11, although the degree of unevenness of the graphite particles is slightly smaller than in Example 10, slight horizontal streaks occurred at the time of printing 5000 sheets under the LL environment, which is a disadvantageous condition for charging uniformity. There was no problem in practical use.

  In Example 12, the degree of unevenness of the graphite particles was slightly smaller than in Example 11, and slight horizontal streaks occurred at the time of printing 3000 sheets under the LL environment, but there was no problem in actual use. Met.

  In Example 13, although Rzjis exceeded 20 μm, a slight horizontal streak that might be caused by dirt occurred at the time of printing 1000 sheets in the LL environment where the surface of the charging roller is particularly susceptible to dirt, but there is no problem in practical use. There was nothing.

  In Example 14, the degree of unevenness of the graphite particles is slightly smaller than that in Example 13, and Rzjis exceeds 20 μm, and a slight horizontal streak that appears to be caused by contamination occurs at the time of printing 5000 sheets in an NN environment. However, there was no problem in practical use.

  In Example 15, the degree of unevenness of the graphite particles is slightly smaller than in Example 14, and Rzjis exceeds 20 μm, and slight horizontal streaks that are thought to be caused by smearing occur at the time of printing 3000 sheets under NN environment. However, there was no problem in practical use.

  In Example 16, Rzjis was less than 2 μm, and although slight horizontal streaks occurred at the time of printing 1000 sheets under the LL environment, which was a disadvantageous condition for charging uniformity, there was no problem in practical use. It was.

  In Example 17, the unevenness degree of the graphite particles is slightly smaller than in Example 16, and Rzjis is less than 2 μm, which is advantageous for charged horizontal stripes at the time of printing 5000 sheets in an NN environment. Although slight horizontal streaks occurred, there was no problem in actual use.

  In Example 18, the degree of unevenness of the graphite particles is slightly smaller than in Example 17, and Rzjis is less than 2 μm, which is advantageous for charged horizontal stripes at the time of printing 3000 sheets in an NN environment. Although slight horizontal streaks occurred, there was no problem in actual use.

  In Comparative Examples 1 and 2, the degree of unevenness of the graphite particles is less than 1.03, the occurrence of horizontal streaks in a part of the image at the time of printing 3000 sheets in the LL environment, and the horizontal streak at the time of printing 5000 sheets. The generated image quality was inferior.

  In Comparative Examples 3 and 4, the degree of unevenness of the graphite particles exceeds 1.08, and horizontal streaks appear in a part of the image at the time of printing 5000 sheets in the NN environment and at the time of printing 3000 sheets in the LL environment. Occurrence was observed. Furthermore, horizontal streaks occurred at the time of printing 5000 sheets under the LL environment, and the image quality was inferior.

  In Comparative Example 5, the generation of horizontal stripes was observed in a part of the image containing no graphite particles and printing 3000 sheets in the NN environment and printing 3000 sheets in the LL environment. Furthermore, horizontal streaks occurred at the time of printing 5000 sheets under the LL environment, and the image quality was inferior.

  In Comparative Example 6, the height of the convex portion was negative, and a dot-like image defect due to overcharging occurred at the time of printing 5000 sheets, which was very inferior. Further, charged horizontal stripes were observed at the time of printing 3000 sheets in the NN environment and 1000 sheets in the LL environment, and the image quality was inferior.

It is explanatory drawing of the unevenness | corrugation degree of the graphite particle cross section of this invention. It is sectional drawing of the charging roller of this invention. It is sectional drawing of another charging roller of this invention. It is sectional drawing of another charging roller of this invention. It is the schematic at the time of the measurement in the apparatus used for the electrical resistance value measurement of the charging roller of this invention. It is the schematic showing the cross section of one embodiment of the electrophotographic apparatus of the present invention. It is the schematic showing the cross section of one embodiment of the process cartridge of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Core metal 2 Elastic layer 3 Surface layer 4 Electrophotographic photoreceptor 5 Charging roller 6 Developing roller 7 Printing medium 8 Transfer roller 9 Fixing part 10 Cleaning blade 11 Exposure 12 Pre-charging exposure device 13 Elastic regulation blade 14 Toner supply rollers 18 and 19 , 20 Power source 21 Intermediate layer 22 Second intermediate layer 30 Toner seal 32 Cylindrical metal 33 Bearing 34 Stabilizing power source 35 Ammeter

Claims (5)

A charging roller that contacts the image carrier and charges the surface of the image carrier;
A metal core, an elastic layer provided on the metal core, and a surface layer provided on the elastic layer;
The surface layer contains a binder, resin particles and graphite particles dispersed in the binder, and has a convex portion derived from the resin particle and a convex portion derived from the graphite particle on the surface. And
The graphite particle-derived convex part having a positive distance between the vertex of the convex part derived from the graphite particle and a plane including three vertexes of the convex part derived from the resin particle adjacent to the convex part derived from the graphite particle Is 80% or more of the total number of convex portions derived from the graphite particles,
A charging roller, wherein the average irregularity degree of the graphite particles forming the projections derived from the graphite particles having the positive distance is 1.03 or more and 1.08 or less. 2. The charging roller according to claim 1, wherein a ten-point average roughness (Rzjis) of the surface of the charging roller and an average interval of unevenness (Sm) of the surface are in the following ranges.
2 μm ≦ Rzjis ≦ 20 μm
15 μm ≦ Sm ≦ 150 μm   The charging roller according to claim 1, wherein the surface layer is formed by applying a coating containing at least the resin particles and the graphite particles to the elastic layer.   4. A process cartridge in which the charging roller and the image carrier according to claim 1 are in contact with each other and are detachable from the main body of the electrophotographic apparatus. .   An electrophotographic apparatus comprising: the charging roller according to claim 1; and an image carrier that is in contact with the charging roller.

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